Thyroid hormones affect nearly all tissues and organs of the body, including the skin. Skin cells contain molecules called thyroid hormone receptors. When thyroid hormones bind to these receptors, cellular activity is increased. People with hypothyroidism, or an underactive thyroid, have an insufficient amount of thyroid hormones and may exhibit skin changes reflecting diminished cellular activity. Some of these changes may cause itching.
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Skin Dryness and Scaling
Approximately 75 percent of people with hypothyroidism have dry skin, according to the medical textbook "Werner and Ingbar’s The Thyroid." When examined under a microscope, the skin of people with hypothyroidism is thin and contains an increased amount of keratin -- a protein found in the uppermost layer of the skin, as well as in hair and nails. The increased keratin and impaired shedding of old cells gives the skin a scaly appearance.
Decreased production of certain fats in the skin may contribute to skin dryness in people with hypothyroidism. Skin dryness with hypothyroidism is often worst on the palms, soles, elbows and knees, although the entire skin surface is typically involved. Dryness and scaling of the skin commonly cause itching. Persistent scratching may lead to open sores and localized infection.
Some people with hypothyroidism develop a severe form of skin scaling known as acquired ichthyosis. This condition represents a very advanced form of the scaling typically seen with hypothyroidism. Itching frequently accompanies the scaling that characterizes acquired ichthyosis.
People with hypothyroidism may exhibit hives, or urticaria, which are characteristically intensely itchy. In a study of 32 people with hypothyroidism published in the "Indian Journal of Dermatology" in 2006, 16 percent exhibited hives. In a larger study of 460 people with hypothyroidism reported in the "Indian Journal of Dermatology" in July-August 2013, 13 percent had hives. The mechanism by which thyroid hormone deficiency provokes hives remains uncertain.
Some people with hypothyroidism have dermatitis herpetiformis, an autoimmune disease characterized by a profoundly itchy, blistering rash. People with this condition often have other autoimmune diseases as well, including autoimmune hypothyroidism. Dermatitis herpetiformis -- which is unrelated to herpes viruses -- typically affects the skin of the back, knees, elbows and buttocks. The rash tends to be similar on both sides of the body.
Reviewed by Mary D. Daley, MD.